Regulatory requirements for temperature sensors used for monitoring industrial processes require that at the point of sale a temperature sensor must be explosion proof (in accordance with specified rules) as a stand alone item. That is, it must not require an additional part to be added to the device to render it in a form that meets regulatory requirements. For this reason, it has long been the practice to supply temperature sensor assemblies in conjunction with thermowells. The thermowells are protective enclosures that may be threaded into a coupling in process equipment, with an opening for insertion of a probe of a temperature sensor. The temperature sensor itself is then inserted into the thermowell, and then remains outside of the process equipment and can provide electrical signals indicative of the temperature in the process equipment. At the point of sale, the thermowell is therefore attached to the temperature sensor.
Customers in the industry have requested a certified stand alone temperature sensor and have specified the size requirements, and the necessity, in some instances, of a straight thread coupling to the thermowell.
In one prior art design of a stand alone temperature sensor made and sold in Canada by Alltemp Sensors, the assignee of the present invention, a thermocouple flame path assembly was provided that included a housing and an exterior nipple threaded into the housing, in which the nipple contained a probe welded or otherwise secured to a sleeve with precision diameter. Leads from the probe extended from the nipple into the housing. The sleeve had a close tolerance fit with the inside diameter of the nipple. While this device was adequate for its purpose, customers still required a certified stand alone device that had a termination head body that enclosed a terminal block.